<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>

</body>
</html>
<script>
    var num = 10;
    alert(1);
     num = 20;
    setTimeout("alert(num)",0);
    alert(3);
    num = 30;
</script>